As with many other aspects of the power industry, deregulation and restructuring are changing how utilities and customers approach power quality monitoring. Traditionalists view PQ monitoring as a reactive process where instruments are deployed on a case-by-case basis to help identify and characterize existing problems. A new approach, however, is fast becoming the standard. This approach incorporates continuous PQ monitoring into the normal assessment of system performance at utilities and customer facilities.
Over the next few pages, we'll discuss the important trends and contributing factors behind this shift toward continuous PQ monitoring. Before we do, though, let's review the different types of PQ monitoring equipment. In general, you can divide monitoring equipment into two broad categories: handheld, portable PQ monitors used for investigations and site surveys and permanently installed systems used to track ongoing power quality performance. Fig. 1 shows a monitoring system that incorporates a wide variety of equipment.
There is still a healthy demand for portable equipment that can be readily moved from location to location. These devices are ideal for site surveys, troubleshooting, or short-term power system performance assessments. They range from simple multimeters to full-feature instruments and fit a variety of needs and budgets. Table 1, on page 24, lists the main types of portable monitoring devices.
Permanently installed power quality monitors come with software and communications capabilities for data collection, data processing, and results presentations. The software maintains a database of system performance information that can be accessed for real-time data or long-term summaries. Table 2, on page 24, summarizes some of the options in this category.
While manufacturers have improved the functionality of power quality monitoring equipment, other contributing factors and recent trends have helped increase the value of permanently installed systems for continuous performance assessment. Let's take at look at them now.
In today's technologically advanced climate, the need for high reliability is essential. Facility personnel define reliability as any problem that causes equipment or processes to misoperate. This includes a wide variety of power quality problems besides traditional power interruptions. Continuous PQ monitoring systems are critical for understanding events that cause power disruptions and evaluating system performance.
Benchmarking expected PQ levels has been an important practice for a number of years. It started with the Electric Power Research Institute's (EPRI) distribution power quality (DPQ) project, which sets PQ standards for power distribution in the United States. Many utilities followed up with their own projects to define expected power quality performance at the local level.
Other countries have also conducted significant benchmarking projects that have become the basis of contracts (e.g., Detroit Edison) and premium power services. Needless to say, setting baselevel requirements is an ongoing process that requires continuous assessment.
Focusing on customers
Utility personnel traditionally determine capital expenditures for system maintenance based on solving problems, handling growth, and maintaining an acceptable level of reliability. A more customer-driven approach, however, considers the costs of system disturbances to end users. In this period of deregulation, such an approach is particularly important. Understanding how power quality variations affect end users requires PQ monitoring and communication with customers.
Power quality data interchange format (PQDIF)
Because utility personnel and customers are now placing new monitoring instruments alongside legacy equipment, there is tremendous interest in data formats that enable different types of instruments to work together. Currently, most software programs for downloading and analyzing data are incompatible with other instruments, making comprehensive analysis difficult or impossible.
In response to this dilemma, EPRI developed the PQDIF, which allows engineers to incorporate a wider range of instruments into their overall systems. Later, the Institute of Electrical and Electronics Engineers (IEEE) established a task force to define a PQDIF standard. To date, several manufacturers have adopted the PQDIF.
Establishment of power quality indices
One of the important advantages of PQ indices (e.g., SAIFI, SAIDI, CAIFI, and CAIDI) is the ability to compare the performance of different systems and track a given system over time in a standardized manner. EPRI defined indices for power quality characteristics as an extension of the DPQ project. The IEEE is currently looking at indices for PQ reporting, especially for voltage sag performance.
New standards for equipment performance
More and more industry groups are recognizing the importance of power quality on equipment operation. As a result, their members have begun to define standards for equipment performance. The Information Technology Industry Council (ITIC) developed a new curve defining the performance of data processing equipment. The semiconductor industry defined a specification for semiconductor manufacturing tools (SEMI F47), and the IEEE defined an overall approach for coordinating equipment performance with supply-system performance (IEEE 1346). Permanently installed monitoring systems can assess system power quality with respect to these standards for convenient evaluation of performance expectations and results.
Facility personnel are interested in monitoring energy use to help identify savings opportunities and assess power-use charges toward different parts of an operation. Engineers can now enhance submetering systems with PQ monitoring capabilities to help identify causes of PQ problems and characterize the performance of individual loads and systems.
Different facilities have different power quality needs. There is substantial interest in developing service contracts tailored to the individual needs of specific customers. PQ monitoring helps establish the necessary benchmarks to facilitate these contracts and becomes an integral part of the implementation. Detroit Edison has demonstrated the viability of including power quality considerations in these contracts.
Internet connectivity and Web interfaces
PQ monitoring is moving toward integrating with the Internet and company Intranets. One manufacturer has built a completely Web-based system. It eliminates the need for software to download and control the monitors by relying on a standard Web browser. All manufacturers, in fact, are working to incorporate Web-interface capabilities into individual instruments or at least central databases. This will make PQ monitoring systems much easier to use and access.
Development of preventive maintenance systems
The ultimate in power quality monitoring are those systems that measure real-time conditions (rather than a maintenance log) and identify problems before they occur. These systems save time and money and provide improved reliability for the overall system. Unlike earlier PQ monitoring equipment, preventive maintenance systems can detect such anomalies as:
- Resonance conditions that may lead to localized harmonic distortion problems.
- Breaker problems that cause restrikes during capacitor switching.
- Arcing conditions caused by bad connections and cable insulation problems.
- Fault-performance problems resulting in high numbers of voltage sags and momentary interruptions.
- Grounding problems resulting in stray voltages and neutral problems.
PQ monitoring systems will play an increasingly important role in preventive maintenance systems because they provide diagnostic- and condition-based information. Electrotek Concepts has organized an interest group to identify and test advanced substation monitoring applications. Many of these applications have already been prototyped and are being used in monitoring systems (e.g., the identification of capacitor-switching problems).
PQ monitoring has come a long way in the past few years. The shift from troubleshooting to predictive analysis and performance assessment has improved response times, saving businesses time and money. This has provided tremendous benefits to an industry where engineers and other technical personnel often have to do more with less.
Mark McGranaghan directs power quality projects and product development at Electrotek Concepts. You can reach him at [email protected].
Sandy Smith manages marketing communications at Electrotek Concepts. He can be reached at [email protected].